Patterns of local adaptation in an insect-plant interaction

The evolution of interactions among species often happens in a geographical mosaic, in which selection, drift and gene flow affect geographically structured populations. If natural selection is a strong factor, local adaptation is expected, meaning that local resident genotypes are expected to have higher fitness than genotypes from other populations. I investigated local adaptation at different geographical scales in the interaction between the alkaloid-bearing legume Crotalaria pallida and its seed predator, the arctiid moth, Utetheisa ornatrix. I studied three populations in southeast Brazil (about 150 Km apart) and compared a Brazilian population to a population from Florida. Larvae from each population were fed fruit from plants from each population in a common garden. At a local scale, there was no significant interaction of plant population and moth population on any of the moth fitness components measured. At a continental scale, moths from Florida and Brazil both had significantly heavier pupa eating their local plant population than when fed on plants from Brazil and Florida, respectively. Local adaptation was observed at a continental geographical scale, but not at a local scale.